2. Introduction
īEtiologic agent of Acquired Immunodeficiency Syndrome
(AIDS).
īDiscovered independently by Luc Montagnier of France and
Robert Gallo of the US in 1983.
īFormer names of the virus include:
īLymphadenopathy associated virus (LAV) (Luc Montagnier)
īHuman T cell lymphotrophic virus (HTLV-III) (Robert Gallo)
īAIDS associated retrovirus (ARV)
ī1986, HIV name was given by International Committee on Virus
Nomenclature.2
3. Introduction
īHIV-2 discovered in 1986, antigenically distinct virus
endemic in West Africa.
ī30 million worldwide are infected. 2 million deaths
every year & 2.5 million new cases every year.
īLeading cause of death of men aged 25-44 and 4th
leading cause of death of women in this age group.
īHIV-1 in humans was believed to be acquired from
chimpanzee (Pan troglodytes troglodytes) by cross species
infections (simian immunodeficiency virus or SIVcpz).
HIV-2 through sooty mangabeys.3
4. Characteristics of the virus
īIcosahedral (20 sided), enveloped virus of
the lentivirus subfamily of retroviruses.
īRetroviruses transcribe RNA to DNA.
īTwo viral strands of RNA found in core
surrounded by protein outer coat.
īOuter envelope contains a lipid matrix within
which specific viral glycoproteins are
imbedded.
īThese knob-like structures responsible for
binding to target cell.4
5. HIV
īThe outer shell of the virus is known as the
Viral enevlope. Embedded in the viral
envelope is a complex protein known as env
which consists of an outer protruding cap
glycoprotein (gp) 120, and gp 41.
īWithin the viral envelope is an HIV protein
called p17(matrix), and within this is the
viral core or capsid, which is made of
another viral protein p24(core antigen).
5
7. Group Specific Antigen (Gag)
īIt encodes for core and shell proteins.
īExpressed as a precursor protein, p55.
īCleaved into p15, p17 and p24.
īp 24 can be detected in serum during early
stages of infection till the appearance of
antibodies.
īThe decline of anti-p24 antibody from
circulation indicates progression of illness and
is an indication of antiviral treatment7
8. Envelope (Env)
īEnvelope (Env) gene codes for envelope
protein gp160; gp120 and gp41.
īgp160 cleaved to form gp120 and gp41.
īgp120 forms the 72 knobs which protrude from
outer envelope.
īgp41 is a transmembrane glycoprotein
antigen that spans the inner and outer
membranes and attaches to gp120.
īgp120 and gp 41 both involved with fusion and
attachment of HIV to CD4 antigen on host cells.
8
9. Polymerase (Pol)
īPolymerase (Pol) codes for viral enzymes
such as reverse transcriptase.
īExpressed as precursor protein p100.
īCleaved into p 31, p 51 and p 64.
īLocated in the core, close to nucleic acids.
īResponsible for conversion of viral RNA
into DNA, integration of DNA into host cell
DNA and cleavage of protein precursors.
9
10. īSexual transmission, presence of
STD increases likelihood of
transmission.
īBlood transfusion.
īParenteral transmission.
īExposure to infected blood or blood
products.
īTransplantation of infected tissues
or organs.
īMother to fetus, perinatal
transmission variable.10
Modes of transmission
12. Types of Exposure and Relative Risk
S.N. Types of Exposure Relative risk per
exposure (%)
1. Sexual intercourse: anal, vaginal, oral 0.1-1.0
2. Transfusion of blood and blood products >90
3. Tissue and organ donations 50-90
4. Injection and injuries 0.5-1.0
5. Mother to baby 30
12
13. Viral Replication
īFirst step, HIV attaches to susceptible
host cell.
īSite of attachment is the CD4 antigen found
on a variety of cells
īhelper T cells
īmacrophages
īmonocytes
īB cells
īmicroglial brain cells
īT cells infected later on.13
14. Early Phase HIV Infection
īIn early phase HIV infection, initial viruses
are M-tropic. Their envelope glycoprotein
gp120 is able to bind to CD4 molecules and
chemokine receptors called CCR5 found on
macrophages.
īMutation of CCR5 in some Europeans are
Completely resistant to HIV infection if the
mutation is homozygous or are susceptible
but progress of AIDS is delayed if the
mutation is heterozygous.
14
Maraviroc
15. īIn late phase HIV infection, most of the
viruses are T-tropic, having gp120
capable of binding to CD4 and CXCR4
found on T-lymphocytes.
15 HIV (arrows) Infecting a T-lymphocyte
16. Life Cycle
īHIV attaches to two cell-
surface receptors (the CD4
antigen and a specific
chemokine receptor).
īThe virus and cell membrane
fuse, and the virion core enters
the cell.
īThe viral RNA and core
proteins are released from the
virion core and are then
actively transported to the
nucleus.
16
17. īThe viral RNA genome is
converted into double-
stranded DNA through an
enzyme unique to viruses,
reverse transcriptase.
īThe double-stranded viral
DNA moves into the cell
nucleus.
īUsing a unique viral
enzyme called integrase,
the viral DNA is
integrated into the cellular
DNA. The integrated
virus is called provirus.
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18. 18
īViral RNA is synthesized by
the cellular enzyme RNA
polymerase using
integrated viral DNA as a
template.
īTwo types of RNA
transcripts shorter spliced
RNA and full-length
genomic RNA are produced.
īShorter spliced RNAs are
transported to the cytoplasm
and used for the production
of several viral proteins that
are then modified in the
ribosomes of the cell.
19. īFull-length
genomic RNAs are
transported to the
cytoplasm.
īNew virion is
assembled and then
buds off.
īMature virus is
released.
19
Enfuvirtide
Indinavir,
Ritonavir,
Darunavir
Raltigravir
Zidovudine
(NRTI)
20. Viral Replication
īThe gp120 protein on virus binds
specifically to CD4 receptor on host cell
with high affinity.
īgp41 causes fusion of the virus to the cell
membrane.
īAfter fusion virus particle enters cell.
īViral genome exposed by uncoating
particle.
īReverse transcriptase produces viral
DNA from RNA.
īBecomes a provirus which integrates into
host DNA.
īPeriod of latency occurs.20
21. Viral Replication
īAfter a period of latency lasting up to
10 years viral replication is triggered and
occurs at high rate.
īCD4 cell may be destroyed in the
process, body attempts to replace lost
CD4 cells, but over the course of many
years body is unable to keep the count at
a safe level.
īDestruction of large numbers of CD4
cause symptoms of HIV to appear with
increased susceptibility to opportunistic
infections, disease and malignancy.
21
22. Clinical Features: According to CDC, clinical course of
HIV infection
īGroup I- Acute HIV infection: Acute onset of fever, malaise, sore throat, myalgia,
arthralgia, skin rash and lymphadenopathy. Viral nucleic acid or viral p24 antigen
may be detected. Antibodies to HIV usually negative. (3 to 6 months)
īGroup II- Asymptomatic infection: Show positive HIV antibody tests and are
infectious. Person usually well.
īGroup III- Persistent generalised lymphadenopathy: Enlarged nodes at two or
more extragenital sites for at least 3 months.
īGroup IV- Symptomatic HIV infection: CD4 T lymphocyte count falls below
400 per cu. mm. Symptoms like diarrhea, fever, weight loss, night sweats and
opportunistic infection develops. Some patients develops AIDS related complex or
conditions.
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23. Primary HIV Syndrome
īCold or flu-like symptoms may occur 6 to 12 weeks after infection.
īSymptoms are relatively nonspecific.
īHIV antibody test often negative but becomes positive within 3 to 6
months (window period), this process is known as seroconversion.
īLarge amount of HIV in the peripheral blood.
īPrimary HIV syndrome resolves itself and HIV infected person
remains asymptomatic for a prolonged period of time, often years
(Clinical Latency).23
24. Clinical Latency Period
īHIV continues to reproduce, CD4 count
gradually declines from its normal value
of 500-1200.
īOnce CD4 count drops below 500, HIV
infected person at risk for opportunistic
infections.
īThe following diseases are predictive of
the progression to AIDS:
īPersistent Herpes-zoster infection
īOral candidiasis (thrush)
īOral hairy leukoplakia (Epstein Barr virus)
īKaposiâs sarcoma (KS) (Herpes Virus)24
Candidiasis
Oral Hairy Leukoplakia
25. Oral Hairy Leukoplakia (OHL)
īBeing that HIV reduces immunologic activity, the
intraoral environment is a prime target for chronic
secondary infections and inflammatory processes,
including OHL, which is due to the Epstein-Barr virus
under immunosuppressed conditions .
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Kaposiâs sarcoma (KS)
īKaposiâs sarcoma is a rare cancer of the blood
vessels that is associated with HIV caused due to
Herpes virus. It manifests as bluish-red oval-shaped
patches that may eventually become thickened.
Lesions may appear singly or in clusters.
OHL
Kaposiâs sarcoma
26. AIDS
īCD4 count drops below 200, person is considered to have advanced HIV disease
īIf preventative medications not started the HIV infected person is now at risk for:
a. Pneumocystis carinii pneumonia (PCP)
b. Cryptococcal meningitis
c. Toxoplasmosis
īIf CD4 count drops below 50:
a. Mycobacterium tuberculosis
b. Cytomegalovirus
c. Lymphoma
d. Dementia
e. Most deaths occur with CD4 counts below 50.
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28. âTypicalâ HIV-1 infection
symptoms
HIV-1 p24 antigen
0 1 2 3 4 5 6 / 2 4 6 8 10
weeks years
HIV antibodies
Time following infection
HIV viral load
HIV proviral DNA
symptoms
âwindowâ
period
1° infection
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29. Immunologic Manifestations
īImmune abnormalities associated with increased viral replication.
īDecrease in CD4 cells due to virus budding from cells, fusion of uninfected cells
with virally infected cells and apoptosis.
īB cells have decreased response to antigens possibly due to blockage of T cell/B
cell interaction by binding of viral proteins to CD4 site.
īCD8 cells initially increase and may remain elevated.
īAs HIV infection progresses, CD4 T cells drop resulting in immunosuppression
and susceptibility of patient to opportunistic infections.
īDeath comes due to immuno-incompetence.29
30. Laboratory Diagnosis of HIV Infection
īMethods utilized to
detect:
īAntibody
īAntigen
īViral nucleic acid
īVirus in culture
30
īScreening tests
īELISA
īRapid test
īHIV spot and comb tests
īSupplemental tests:
īWestern blot test
īIndirect immunofluorescence test
īRadio Immuno assay
īPCR
31. ELISA Testing
īAntibodies detected in ELISA include those directed against: p24, gp120, gp160
and gp 41, detected first in infection and appear in most individuals.
31
Other Screening Tests
īAgglutination tests using latex particles, gelatin particles or microbeads are
coated with HIV antigen and will agglutinate in the presence of antibody.
īDot-Blot Testing utilizes paper or nitrocellulose impregnated with antigen,
patient serum is filtered through, and anti-antibody is added with enzyme
label, color change is positive.
īA rapid, cost-effective and may become an alternative to standard ELISA
and Western blot testing.
32. Western Blot
īMost popular confirmatory test.
īAntibodies to p24 and p55 appear
earliest but decrease or become
undetectable.
īAntibodies to gp31, gp41, gp 120,
and gp160 appear later but are
present throughout all stages of the
disease.
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īInterpretation of results.
īNo bands, negative.
īIn order to be interpreted as positive a minimum of 3 bands directed against the
following antigens must be present: p24, p31, gp41 or gp120/160.
īCDC criteria require 2 bands of the following: p24, gp41 or gp120/160.
33. Detection of p24 HIV antigen
īMost useful for the following:
īearly infection suspected in seronegative patient
īNewborns
īMonitoring disease progress
33
Polymerase Chain Reaction (PCR)
īLooks for HIV DNA in the WBCs of a person.
īPCR amplifies tiny quantities of the HIV DNA present, each cycle of PCR
results in doubling of the DNA sequences present.
34. Virus isolation
īVirus isolation can be used to definitively diagnose
HIV.
īBest sample is peripheral blood, but can use CSF,
saliva, cervical secretions, semen, tears or material
from organ biopsy.
īCell {peripheral blood mononuclear cell (PBMC)}
growth in culture is stimulated, amplifies number of
cells releasing virus.
īCultures incubated one month, infection confirmed
by detecting reverse transcriptase or p24 antigen in
supernatant.
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35. Resistance:
īTemperature: Inactivated at 56o
C in 30 minutes and in seconds at 100o
C.
īDisinfection:
ī35% Isopropyl alcohol: inactivation in 10 minutes.
ī70% ethanol
ī0.5% lysol
ī2% freshly prepared glutaraldehyde
ī0.5% sodium hypochlrite
ī3% hydrogen peroxide
īExtremes of pH (pH 1.0, pH 13.0)
īResistant to Lyophilisation
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